"The one thing that's very clear, and there's no doubt about this, is its extraordinary capability of spreading," Fauci was quoted as saying on NBC News, referring to the Omicron variant.

 

"It is just raging through the world, really." He said Omicron is likely to overtake the Delta variant in the US.

 

According to the World Health Organisation (WHO), Omicron has been detected in 89 countries. It is spreading significantly faster than the Delta variant, the agency said, including in countries with high levels of population immunity. The variant already accounts for the majority of cases in the UK.

 

"Our hospitals, if things look like they're looking now, in the next week or two, are going to be very stressed with people," Fauci, the director of the National Institute for Allergies and Infectious Diseases, was quoted as saying to ABC news on Sunday.

 

"We have so many people in this country who are eligible to be vaccinated who have not yet been vaccinated. And that's going to be a real problem for stress on the hospital system," he warned.

 

The warning comes as Covid-19 infections in America have spiked over the past week: both New York State and the District of Columbia have reported successive days of record cases. The risk of infection is particularly high for those among Americans who are either unvaccinated or did not receive a booster shot.

 

Further, according to early data, the Omicron variant might cause less severe disease than Delta. However, public health and infectious disease experts caution that it is too early to tell, because hospitalisations in the UK and South Africa -- with high Omicron cases -- continue to rise. Thus, the WHO has also noted that the variant could surge hospital admissions even if it is less severe.

 

"When you have so many, many infections, even if it is less severe, that overcomes this slight to moderate diminution in severity," Dr. Fauci said.

 

Yet Fauci said that he didn't anticipate the US moving toward broad shutdowns.

 

"I don't foresee the kind of lockdowns that we've seen before, but I certainly see the potential for stress on our hospital system," he said.

 

White House officials have so far ruled out any new travel restrictions, though the US does now require a Covid test within one day of travelling to America. Fauci also urged Americans to be "prudent" with their holiday plans and to "wear masks in airports and on planes".

 

According to data from the US Centers for Disease Control and Prevention, the country is now averaging more than 125,000 new Covid-19 cases a day. The US continues to be the worst-hit country with the world's highest number of cases and deaths at 50,846,828 and 806,439, according to Johns Hopkins University.